CUPRITE: Onganja, South Africa (48.07)
Cuprite is one of the rarest of all gems. For all practical purposes, cuttable material comes from only one locality. Only good crystals or pieces of crystals are cuttable, however, as other material from this mine is opaque. Mineral collectors do not wish to see their fine crystals cut, limiting the supply of available faceting material. Cut gems have a metallic appearance and magnificent deep red color. There are unwearable, but among the most beautiful of all gems and someday may be extremely rare in the marketplace.
Cuprite Value
The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.
Cuprite Information
| Data | Value |
| Name | Cuprite |
| Crystallography | Isometric. Crystals, cubes, and octahedra, or combinations; also needlelike, in densely Packed mats called chalcotrichite with no gem significance. |
| Colors | Brownish red, red, purplish red, nearly black. |
| Luster | Adamantine to submetallic; earthy. |
| Hardness | 3.5-4 |
| Cleavage | Poor. Fracture conchoidal to uneven. Brittle. |
| Stone Sizes | Largest mass of cuttable cuprite (PC) is completely transparent and weighs 2 kg. Before the amazing Onganja discovery, the largest stones were less than 1 carat, as only tiny crystals had ever been found. Onganja stones have been cut up to 300 carats, are flawless, and potentially could be much larger. Smithsonian Institution (Washington, D.C): 203.75 (octagon, Namibia); 172, 125.5, 110 (red, Namibia). Royal Ontario Museum (Toronto, Ontario, Canada): 66.34 (oval, Namibia). Private Collection: 299.5 (oval, Namibia). Devonian Group (Calgary, Alberta, Canada): 48.6 (red, Namibia). |
| Luminescence | None. |
| Formula | Cu20. |
| Pleochroism | Sometimes anomalously pleochroic. |
Streak: Brownish red.
Optics: 6.14; Namibia = 6.0-6.07.
Optics: N= 2.848.
Occurrence: Secondary mineral in copper deposits. Usually microscopic crystals.
Arizona: New Mexico; Pennsylvania; Colorado; Utah; Idaho.
Mexico; Bolivia; Chile; France; USSR; Zaire; Japan: other locations.
Onganja, Namibia: unique occurrence, with crystals up to more than 6 inches across, blood red and transparent; often coated with green malachite.
Comments: Cuprite is one of the rarest of all gems. For all practical purposes, cuttable material comes from only one locality. Only good crystals or pieces of crystals are cuttable, however, as other material from this mine is opaque. Mineral collectors do not wish to see their fine crystals cut, limiting the supply of available faceting material. Cut gems have a metallic appearance and magnificent deep red color. There are unwearable, but among the most beautiful of all gems and someday may be extremely rare in the marketplace.
Name: From the Latin cuprum (copper), in allusion to the composition.
